Vehicle combinations comprising a tractor unit with a trailer are generally equipped with both parking brakes and service brakes. In the case for example of timber carriers it is usual in certain regions, particularly when loading timber, to only activate parking brakes with which the tractor vehicle is provided, whereas the trailer onto which the timber is being loaded is not braked. The risk of wheels of the trailer being pressed down too deeply into the running surface on which it is at the time may thus be reduced, in which case no service brakes of the tractor vehicle or the trailer need be activated.
When loading a vehicle combination, e.g. a timber carrier, in situations where the running surface slopes, undesired vehicle movements may occur, potentially causing the trailer alone or the whole vehicle combination to begin to slide and/or roll in cases where too great a load is applied on the trailer. In certain cases the brake action applied will quite simply be insufficient. In other cases there may be too little friction between the vehicle's wheels and the running surface to keep the vehicle stationary. Loading the trailer when the vehicle combination is on a hill may in particular be hazardous if the running surface is more or less slippery, e.g. icy, muddy or wet. It should be noted that there are many applications in which a driver/operator will not be in a vehicle cab but will instead be operating a loading device, e.g. a crane device, or in other situations be in the immediate vicinity of said vehicle combination. In such situations said undesired vehicle movements may entail risk of injury or in the worst case direct danger to the life of said operator or other persons in the vehicle's surroundings. Undesired movements of the vehicle combination during loading/unloading might of course also result in damage to the vehicle combination or objects in its surroundings.
DE102011118169 describes a vehicle where an empty trailer is intended to be loaded on the actual tractor unit. When loading timber, a parking brake of the tractor vehicle is activated. In this situation said trailer is loaded by the tractor unit and allowed to roll rearwards away from said tractor vehicle. When the trailer has rolled a certain desired/appropriate distance it is braked for suitable positioning relative to said tractor vehicle. Timber loaded is secured to, and thus serves en route as a connection between, said trailer and said tractor vehicle.